In the control of internal combustion engines, the conventional practice utilizes electronic control units having volatile and non-volatile memory, input and output circuitry, and a processor capable of executing an instruction set. The electronic control unit controls the various functions of the engine and associated systems. A particular electronic control unit communicates with numerous sensors, actuators, and sometimes with other electronic control units to control various functions and operating parameters of the engine. For example, an electronic control unit may control various aspects of fuel deliver, including the engine idle speed.
An existing method and apparatus for maintaining vehicle battery charge by controlling engine idle speed is described in U.S. Pat. No. 5,402,007, issued to Center et al. In this existing system, an alternator driven by the engine supplies power to drive electrical loads and to charge a vehicle battery. The system adaptively learns a system voltage set point. Thereafter, idle speed is controlled in response to the regulation state of the electrical system to preferably maintain the system in set point regulation, ensuring adequate battery charge or minimal battery discharge.
Because newer vehicles typically have greater system electrical loads than older vehicles, the details of the battery charging system are becoming more important. A higher engine idle speed may maintain battery charge during heavier electrical loads, but on the other hand, results in less fuel economy. Further, although existing battery charge maintenance systems are used in some applications that are commercially successful, the increasing electrical loads in vehicles and concerns about fuel economy create a need for an improved engine control method with more functionality in the charging subsystem than existing methods.